You should give the detail about your camera setup. Otherwise it's hard for people to figure it out what's the problem. yuxuan <table width=100%> <tr valign=top> <td> <td>j.hartmann@dkfz-heidelberg.de Sent by: gate-users-bounces@lists.healthgrid.org 03/02/2007 07:20 AM <td>                To:        Gate users <gate-users@lists.healthgrid.org>         cc:                 Subject:        [Gate-users] strange counting rates</table> <tt>Hi gate users, I have a problem with the counting rates of my simulation data. I simulate two opposing pet heads which are rotating around the isocentre in steps of 10 degrees. The source is a circle with a radius of 1 cm positioned at the isocentre. What I don`t understand are the counting rates: Although the counting rates for each scanner position should be roughly the same because of the symmetry, I get peaks at the angles 45 and 135. The number of detected events at these angles is 20% higher than the number at 0,90 and 180 deg. I think there must be something wrong with my simulation setup, but I really don`t have any idea what this could be. For the scanner rotation, I use "orbiting" and for the source, I fixed the angle theta so that the emission takes place only in the xy-plane, but that shouldn`t be the problem, as I have the same peaks in the data resulting from simulations with not fixed theta. Does anybody have an idea where the problem could be? Cheers, Julia _______________________________________________ Gate-users mailing list Gate-users@lists.healthgrid.org http://lists.healthgrid.org/mailman/listinfo/gate-users </tt>